Frank Taylor

Determining the Cost of Producing Ethanol from Corn Starch and Lignocellulosic Feedstocks

The mature corn-to-ethanol industry has many similarities to the emerging lignocellulose-to-ethanol industry. It is certainly possible that some of the early practitioners of this new technology will be the current corn ethanol producers. In order to begin to explore synergies between the two industries, a joint project between two agencies responsible for aiding these technologies in the Federal government was established. This joint project of the USDA-ARS and DOE/NREL looked at the two processes on a similar process design and engineering basis, and will eventually explore ways to combine them. This report describes the comparison of the processes, each producing 25 million annual gallons of fuel ethanol. This paper attempts to compare the two processes as mature technologies, which requires assuming that the technology improvements needed to make the lignocellulosic process commercializable are achieved, and enough plants have been built to make the design well-understood. Ass umptions about yield and design improvements possible from continued research were made for the emerging lignocellulose process. In order to compare the lignocellulose-to-ethanol process costs with the commercial corn-to-ethanol costs, it was assumed that the lignocellulose plant was an Nth generation plant, built after the industry had been sufficiently established to eliminate first-of-a-kind costs. This places the lignocellulose plant costs on a similar level with the current, established corn ethanol industry, whose costs are well known. The resulting costs of producing 25 million annual gallons of fuel ethanol from each process were determined. The figure below shows the production cost breakdown for each process. The largest cost contributor in the corn starch process is the feedstock; for the lignocellulosic process it is the capital cost, which is represented by depreciation cost on an annual basis.

Dry-grind process for fuel ethanol by continuous fermentation and stripping.

Conversion of a high‐solids saccharified corn mash to ethanol by continuous fermentation and stripping was successfully demonstrated in a pilot plant consuming 25 kg of corn per day. A mathematical model based on previous pilot plant results accurately predicts the specific growth rate obtained from these latest results. This model was incorporated into a simulation of a complete dry‐grind corn‐to‐ethanol plant, and the cost of ethanol production was compared with that of a conventional process. The results indicate a savings of

Economic analysis of fuel ethanol production from corn starch using fluidized-bed bioreactors.

0.03 per gallon of ethanol produced by the stripping process. The savings with stripping result from the capacity to ferment a more concentrated corn mash so there is less water to remove downstream.

Fermentation and costs of fuel ethanol from corn with quick-germ process

Abstract The economics of fuel ethanol production from dry-milled corn starch were studied in fluidized-bed bioreactors (FBRs) using immobilized biocatalysts. Glucoamylase immobilized on porous diatomaceous earth was used for hydrolysis of the starch to glucose in a packed-bed reactor. The fermentation of glucose to ethanol was carried out in FBRs using Zymomonas mobilis immobilized in κ -carageenan beads. Volumetric ethanol productivities of up to 24 g/l h were achieved in non-optimized laboratory-scale systems. For a 15 million gal/yr ethanol plant, an economic analysis of this process was performed with Aspen Plus (Aspen Technology, Cambridge, MA) process simulation software. The analysis shows that an operating cost savings in the range of 1.1–3.1 cents/gal can be realized by using the FBR technology.

Continuous high-solids corn liquefaction and fermentation with stripping of ethanol

The Quick-Germ process developed at the University of Illinois at Urbana-Champaign is a way to obtain corn oil, but with lower capital costs than the traditional wet-milling process. Quick-Germ has the potential to increase the coproduct credits and profitability of the existing dry-grind fuel ethanol process, but the fermentability of the corn remaining after oil recovery has not been tested. Therefore, a series of pilot scale (50 L) fermentations was carefully controlled and monitored with unique methods for standard inoculation and automatic sampling. It was found that the concentration of suspended solids was significantly reduced in the Quick-Germ fermentations. When compared at the same concentration of fermentable sugars, the fermentation rate and yield were not statistically different from controls. When Quick-Germ was integrated into a state-of-the-art dry-grind fuel ethanol process, computer simulation and cost models indicated savings of approx

Kinetics of continuous fermentation and stripping of ethanol

0.01/L of ethanol (

Effects of ethanol concentration and stripping temperature on continuous fermentation rate

0.04/gal) with the Quick-Germ process. Additional savings associated with the lower suspended solids could not be quantified and were not included. However, the savings are sensitive to the price of corn oil.

Scale-up of ethanol production from winter barley by the EDGE (enhanced dry grind enzymatic) process in fermentors up to 300 l.

Removal of ethanol from the fermentor during fermentation can increase productivity and reduce the costs for dewatering the product and coproduct. One approach is to recycle the fermentor contents through a stripping column, where a non-condensable gas removes ethanol to a condenser. Previous research showed that this approach is feasible. Savings of

Control of packed column fouling in the continuous fermentation and stripping of ethanol

0.03 per gallon were predicted at 34% corn dry solids. Greater savings were predicted at higher concentration. Now the feasibility has been demonstrated at over 40% corn dry solids, using a continuous corn liquefaction system. A pilot plant, that continuously fed corn meal at more than one bushel (25 kg) per day, was operated for 60 consecutive days, continuously converting 95% of starch and producing 88% of the maximum theoretical yield of ethanol. A computer simulation was used to analyze the results. The fermentation and stripping systems were not significantly affected when the CO(2) stripping gas was partially replaced by nitrogen or air, potentially lowering costs associated with the gas recycle loop. It was concluded that previous estimates of potential cost savings are still valid.

Corn-milling pretreatment with anhydrous ammonia

A pilot plant consisting of a 30-liter fermenter, and a 10-cm packed column with a blower and condenser to recover ethanol vapors was operated continuously for 185 days. On-line washing of the packing in the column twice weekly with condensed ethanol from the process (approximately 45% v/v) controlled fouling by attached yeast cells. Steady-state glucose consumption rates of up to 800 gh-1, condensed ethanol production rates of up to 26 l/day, and consistently high ethanol yield of approximately 0.50 gg-1 glucose were observed. Data from the pilot plant showed that the primary inhibitory effect of ethanol on the steady-state fermenter performance was to decrease the cell yield, while the specific glucose consumption rate was almost unaffected by ethanol concentrations up to 65 gl-1. A new kinetic model is introduced to represent these effects.